scholarly journals Characterization of Wrapped Coil Tank Water Heater During Charging/Discharging

2017 ◽  
Author(s):  
Ahmed Elatar ◽  
Kashif Nawaz ◽  
Bo Shen ◽  
Van Baxter ◽  
Omar Abdelaziz
Keyword(s):  
Water Temperature ◽  
Heat Pump ◽  
Thermal Stratification ◽  
Water Tank ◽  
Water Heater ◽  
Water Heaters ◽  
Discharge Flow Rate ◽  
Circulation Patterns ◽  
The Impact ◽  
Supply Water

Heat pump water heaters (HPWH) are an energy efficient method for water heating compared to conventional electric water heaters. A wrapped coil around the water tank is often used as the condenser for the heat pump for such applications. Thermal stratification, caused by varying heat transfer rate from the condenser to the water depending on the phase of the refrigerant and the wrap configuration, is often observed inside the tank, especially for HPWHs using CO2 as the refrigerant. The current study investigates the impact of the charging/discharging process on thermal stratification. A series of simulations were conducted based on the draw patterns recommended by the DOE method of test for rating water heater performance. We also analyzed the water circulation patterns during charging/discharging process. The thermal stratification was adversely affected because of the circulation even when the Heat Pump (HP) was operational. It was observed that a relatively higher charge/discharge flow rate disrupts the thermal stratification quickly and thus lowers the supply water temperature. Furthermore, the duration of charging/discharging also plays an important role. It was noticed that the back flow has insignificant effect on the supply water temperature if charging/discharging time is relatively small. However, the effect was obvious for larger water draw flow rates that last for longer time.

CFD Solution and Experimental Testing of Buoyancy-Driven Convection Caused by Condensers Immersed in a Water Tank of HPWH

2003 ◽  
Author(s):  
Zhiming Gao ◽  
Viung C. Mei ◽  
Fang C. Chen
Keyword(s):  
Water Temperature ◽  
Heat Pump ◽  
Cfd Simulation ◽  
Experimental Testing ◽  
Electricity Consumption ◽  
Water Tank ◽  
Water Heater ◽  
Water Heaters ◽  
C 30 ◽  
Tube Condenser

Heat pump water heaters can cut electricity consumption, comparing with the conventional electric resistant water heating tanks by half. A conventional heat pump water heater (HPWH) requires a water circulating pump to sample water temperature every 15 minutes in the tank and to draw water to a condenser-water heat exchanger outside the tank, if water temperature is below the set point. The pump would be on at least once every 15 minutes, 24 hours a day. The novel design presented in this study was to insert the condenser coil through the opening on the top of the water tank. This design eliminated the need of the water circulating pumps, and thus greatly improved the reliability of the HPWH systems. Two types of condenser coil designs were considered; one was a bayonet tube (tube-in-tube) and one was the “U” tube. Previous test data indicated that “U” tube design performed better than the bayonet tube condenser coil, and thus only “U” tube condenser coil was considered in the study. With straight “U” tubes inserted into the tank, it was found that the convective heat transfer was not strong enough to break water temperature stratification in the tank, which resulted in a temperature differential of 16°C (30°F) from top to bottom. However, when the coil was built in “L” shape, the water stratification disappeared. A computational fluid dynamics code, CFD, was used to study the straight and L shaped condenser coils. Results from CFD simulation were compared with the experimental data and found they were close to each other.

Optimal Supply Water Temperature Control of Water Source Heat Pump

Solar Energy ◽  
2005 ◽  
Author(s):  
M. Palahanska-Mavrov ◽  
G. Wang ◽  
M. Liu
Keyword(s):  
Potential Energy ◽  
Water Temperature ◽  
Heat Pump ◽  
Temperature Control ◽  
Energy Cost ◽  
Energy Savings ◽  
Water Source ◽  
Theoretical Models ◽  
The Impact ◽  
Supply Water

The water loop supply water temperature is the most critical control parameter for operating energy cost in water source heat pump systems. In this paper, the impact of the water loop temperature on operating energy cost is investigated for different types of buildings under different loads using theoretical models. The theoretical models and approaches are also applied to an 80,000 square feet office building to determine the building heating and cooling load, optimal supply water temperature, and potential energy cost savings based on measured supply water temperature and loop heat gain. It is concluded that the optimal supply water temperature control can significantly reduce the annual energy costs associated with compressor power and boiler energy. The potential energy savings is determined to be 24% in the application building.

Development of Ammonia-Water Absorption Heat Pump Water Heater for Residential and Commercial Applications

2013 ◽  
Author(s):  
Michael Garrabrant ◽  
Roger Stout ◽  
Paul Glanville ◽  
Chris Keinath ◽  
Srinivas Garimella
Keyword(s):  
Natural Gas ◽  
Heat Pump ◽  
Operating Conditions ◽  
System Level ◽  
Outer Diameter ◽  
Water Heater ◽  
Absorption Heat Pump ◽  
Water Heaters ◽  
Commercial Applications ◽  
The Impact

Approximately half of the water heaters sold in the U.S. and Canada for residential and small commercial applications are natural gas fired storage water heaters, with a maximum theoretical thermal efficiency of 96%. A packaged water heater heated by a 2.9 kW absorption heat pump was designed and demonstrated in this study to achieve performance exceeding these limitations. The modeling and validation of the absorption cycle and of the natural gas-fired combustion system are discussed here. Heat transfer characteristics of the absorption components at expected operating conditions were used to model cycle performance. A single-effect system based on these models was fabricated and yielded a cyclic COP of 1.63, within 3% of predictions. A corresponding GAX cycle-based system yielded performance 20% lower than predicted values, indicating the need for larger heat and mass exchangers to achieve the expected system level performance. The gas-fired burner configuration required for this heat pump is governed by the water heater envelope, desorber geometry and process requirements, coupled with emissions requirements. Parametric CFD analyses were conducted to estimate the impact of chamber design on burner performance, and revealed a beneficial recirculation pattern within the combustion chamber that was strongly influenced by chamber height. Emission reductions depended on chamber diameter, and prototype burners with smaller outer diameter fabricated based on these designs met emission targets.

Numerical Investigation of Thermal Separators Within the Evacuated Tubes of a Water-in-Glass Solar Water Heater

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Asif Soopee ◽  
Abdel Anwar Hossen Khoodaruth ◽  
Anshu Prakash Murdan ◽  
Vishwamitra Oree
Keyword(s):  
Tilt Angle ◽  
Thermal Efficiency ◽  
Thermal Stratification ◽  
Maximum Deviation ◽  
Water Tank ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water ◽  
Thermal Distribution ◽  
Evacuated Tubes

The effects of thermal separators within the evacuated tubes of a water-in-glass solar water heater (SWH) were numerically investigated using the commercial computational fluid dynamics (CFD) software ANSYS fluent. To validate the three-dimensional (3D) model, an experiment was performed for the passive operation of the SWH for a fortnight period, of which 3 h of recorded data was selected. The Boussinesq's approximation was employed, and the respective solar irradiance and ambient temperature profiles were incorporated. A maximum deviation of only 2.06% was observed between the experimental and numerical results. The model was then adapted for the case where thermal separators are inserted within the evacuated tubes of the SWH and both cases were run for two tilt angles, 10 deg and 40 deg. The temperature and velocity profiles within the evacuated tubes were analyzed alongside the temperature contours, thermal stratification, and overall thermal efficiency of the SWH. At a 40 deg tilt, without thermal separators, the flow streams within the evacuated tubes are restrained, and a chaotic thermal behavior was observed, thereby restricting thermal distribution to the water stored in the SWH tank. A lower tilt angle (10 deg) provided a more desirable thermal distribution. With thermal separators, however, the tilt angle preference was reversed. A faster and more uniform thermal distribution was achieved within the water tank, with a sizeable reduction in the thermal stratification at a 40 deg tilt. The overall thermal efficiency of the SWH was improved by 4.11% and 4.14% for tilt angles of 10 deg and 40 deg, respectively.

Evaluation of Passive Anti-Fouling Technology Applied to CO2 Heat Pump Water Heaters

2014 ◽  
Author(s):  
Portia Murray ◽  
Stephen J. Harrison ◽  
Ben Stinson
Keyword(s):  
Heat Transfer ◽  
Water Supply ◽  
Heat Pump ◽  
Hot Water ◽  
Normal Operation ◽  
Mineral Deposits ◽  
Reverse Direction ◽  
Water Tank ◽  
Flow Rates ◽  
Water Heaters

Heat pump water heaters are increasing in popularity due to their increased energy efficiency and low environmental impact. This paper describes the experimental testing of a transcritical CO2 heat pump water heater at Queen’s University. A modified 4.5 kW Eco-Cute unit was studied. It sourced heat from a constant temperature water supply and rejected the heat to a 273 litre hot water tank through a gas-cooler. The high temperatures that occur in the gas-cooler of this unit make it ideally suited for natural convection, (i.e., thermosyphon) circulation on the potable water side. This has the potential to reduce pumping power, simplify system operation and design, and increase thermal stratification in the hot water storage tank. This configuration, however, is susceptible to the accumulation of sediments, scale and mineral deposits (i.e., fouling) in geographic regions where high mineral deposits may be present in the water supply. To counteract fouling in these cases, a passive back-flushing system was proposed to prevent the accumulation of deposits on the heat transfer surfaces of the gas-cooler. As hot water is drawn from the system, the cold “mains” supply water is directed through the gas-cooler in the reverse direction of normal operation, scouring the heat transfer surfaces and dissolving deposits of inverse-soluble salts which are a major contributor to fouling on hot heat transfer surfaces. The gas-cooler used was a specially designed unit that, although offering high performance in a compact unit, may be susceptible to the fouling and blockage of the heat transfer passages when used at thermosyphon flow rates. Experiments were conducted to evaluate the effects of the back-flush operation on heat pump performance (i.e., COP) and operation. These were conducted under controlled laboratory conditions, at a range of draw flow rates and temperatures, and are summarized in this paper.

scholarly journals Comparison of Transcritical CO2 and Conventional Refrigerant Heat Pump Water Heaters for Domestic Applications

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 479
Author(s):  
Ignacio Paniagua ◽  
Ángel Álvaro ◽  
Javier Martín ◽  
Celina Fernández ◽  
Rafael Carlier
Keyword(s):  
Heat Pump ◽  
Thermodynamic Cycle ◽  
Heat Pumps ◽  
Design Tool ◽  
Operating Conditions ◽  
Hot Water ◽  
Coefficient Of Performance ◽  
Ambient Conditions ◽  
Water Heater ◽  
Water Heaters

Although CO 2 as refrigerant is well known for having the lowest global warming potential (GWP), and commercial domestic heat pump water heater systems exist, its long expected wide spread use has not fully unfolded. Indeed, CO 2 poses some technological difficulties with respect to conventional refrigerants, but currently, these difficulties have been largely overcome. Numerous studies show that CO 2 heat pump water heaters can improve the coefficient of performance (COP) of conventional ones in the given conditions. In this study, the performances of transcritical CO 2 and R410A heat pump water heaters were compared for an integrated nearly zero-energy building (NZEB) application. The thermodynamic cycle of two commercial systems were modelled integrating experimental data, and these models were then used to analyse both heat pumps receiving and producing hot water at equal temperatures, operating at the same ambient temperature. Within the range of operation of the system, it is unclear which would achieve the better COP, as it depends critically on the conditions of operation, which in turn depend on the ambient conditions and especially on the actual use of the water. Technology changes on each side of the line of equal performance conditions of operation (EPOC), a useful design tool developed in the study. The transcritical CO 2 is more sensitive to operating conditions, and thus offers greater flexibility to the designer, as it allows improving performance by optimising the global system design.

A New Performance Estimate Method for Design of Storage-Type Domestic Electrical Water-Heaters Based on the CFD Simulation

2010 ◽  
Vol 129-131 ◽  
pp. 463-466
Author(s):  
Li Li Zhao ◽  
Zhi Jun Zhang ◽  
Shi Wei Zhang
Keyword(s):  
Water Temperature ◽  
Cfd Simulation ◽  
Cold Water ◽  
Discharge Rate ◽  
Water Discharge ◽  
Hot Water ◽  
New Method ◽  
Dynamics Simulation ◽  
Water Heater ◽  
Water Heaters

The 3D physical model of the electrical water heater was built. The water-heater performance was resolved by computer fluid dynamics simulation (CFD). The heater performance is characterized by a new method rather than that the discharge efficiency, extraction efficiency and fraction of heat recoverable. The new method is based on the constant discharge water temperature and rate for end user, 5L/min and 43°C that include the hot water from EWH and cold water from outside EWH. But the water discharge rate from EWH was variable as the water temperature discharge from EWH was variable. Compared with the traditional method, it is more close to the user using reality condition.

Statistical Analyses on Usage of Water Heater in Urban Residential Buildings

2014 ◽  
Vol 521 ◽  
pp. 748-751
Author(s):  
Zhao Xia Zhou
Keyword(s):  
Energy Consumption ◽  
Heat Pump ◽  
Residential Buildings ◽  
Water Heater ◽  
Water Heaters ◽  
Heat Pump Water Heater ◽  
Initial Cost ◽  
The Common ◽  
The Cost ◽  
Residential Water

A survey for water heater in urban residential buildings is carried in Wuhan. The results show that more than 40% subjects use solar energy water heat. More than 20% subjects point out the energy consumption of water heater should be decreased. There are about 24.8% subjects take initial cost as the first place when they chose water heater. 44.2% subjects know about heat pump water heater, but they could not buy it if the initial cost is too high. There are 84% subjects could select heat pump water heater when the cost is no more 20% high than the average price of the common water heaters. Moreover, the energy consumptions of residential water heaters are also investigated. The energy consumption characteristics of water heater in Wuhan are analyzed.

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